The transfer of powders from a bulk supply to smaller containers for marketing or storage is complicated by the fact that the flow characteristics of powders are very different from those of liquids. For example some powders tend to be sticky and flow only with difficulty whilst others may be of a very light and flocculent nature so that when they are poured into a container air which is displaced carries with is substantial quantities of entrained powder. This can cause fire hazards if the powder is flammable or financial loss and danger to health if the powder is expensive or toxic.
The filling of a large number of containers with powder from a bulk supply must for practical reasons be carried out rapidly and under conditions so that preferably the escape of powder is prevented or if this is not possible then efficient methods of powder recovery are employed. Various measures have been employed for the purposes of achieving this objective. For example one of these involves fitting the delivery end of a conduit extending from the bulk supply of powder to be transferred to the container to be filled with an inflatable annulus which can be inflated and made to grip and form an air-tight seal with the mouth of the container. A second conduit is then provided between external wall of the inlet conduit and the inflatable annulus through which displaced air containing entrained powder can pass on its way to a powder recovery station where powder can be recovered. In order to assist the process a draught created by an exhaust fan assists the removal of displaced air. However in order to avoid any excessive reduction in pressure within the container air from outside the container is allowed to enter the container through a third conduit and merge with the effluent stream of air leaving the container.
In this way an improvement has been effected in transferring powder. However this technique results in excessive quantities of powder being carried from the container to the removal recovery plant. Furthermore the conduit from the container to the plant tends to have powder deposited in it. We have now discovered that both problems can be overcome to a significant extent if the inlet for the scavenging stream of air and the outlet for the displaced air are located close together within the container. In this way a sufficiently vigorous stream of air can be passed through the conduit to prevent deposition of powder within the conduit without a major disturbance of powder already in the container. As a consequence removal of large quantities of powder in the air stream can be prevented. This has the further advantage in that since apparati for filling containers from bulk supply are generally required to be programmed to deliver predetermined weights of material we have found that as a result of the present invention we are able to programme the apparati to deliver such quantities more accurately.